This invention relates to the longitudinal compressional treatment of flexible web materials such as knitted and woven textile fabrics, papers, plastic films, and so-called "non-wovens", the latter being of natural or synthetic substance formed into webs, e.g., as by air laying or wet laying of fibers.
In the laboratory from which the present invention comes, we have devoted many years to development of the treatment of webs in which longitudinal compressional forces are applied in the plane of the flexible web material. From this work has come a number of inventions, including the compactor, U.S. Pat. Nos. 2,765,513 and 2,765,514; the bladed microcreper, U.S. Pat. Nos. 3,260,778 and 3,426,405; the bladeless microcreper, U.S. Pat. Nos. 3,810,280, 3,869,768 and 3,975,806; and the two roll microcreper, U.S. Pat. No. 4,142,278. As implemented by most of these inventions, the untreated web is driven longitudinally by using a low friction surface to press the web against a rotating drive roll and then, within a short distance of the drive point, retarding forces are applied to the traveling web. The opposition between the driving and retarding forces, while the material remains confined face-wise, produces desirable physical change in the web material, for instance, increase in its bulk, thickness and elasticity.
In the case of textile and textile-like materials, the web can be compacted longitudinally within its own plane, without folding of the web upon itself or formation of crepe, but with crimping in situ of the tiny individual fibers ("microcreping" of the fibers) that make up the threads or yarns of the fabric.
In the case of solid thin sheets such as paper or plastic film, the longitudinal compressive treatment can form barely perceptible undulations oz crepes in the web as a whole ("microcreping" of the web), in which the overall appearance of the faces of the web is still one of smoothness, without superficial coarse crepe or folds being present. If, however, coarse crepe is desired, this can be achieved by suitable enlargement of the treatment cavity.
In many cases desirable qualities produced by the longitudinal treatment remain in the web after some or even all of the compression in length of the web is removed by stretching.
In specific examples, the treatment can increase the softness or drapability of a web, increase its covering effect and opacity, make the surface texture of the web more appealing, render the web shrinkproof, apply decorative effects to the web, or cause components of the web to be more intimately interengaged in a way that is useful. Paper webs can be made stretchy and have their burst resistance improved.
With respect to many materials, the machine and process that has shown most promise employs an angled retarder/flexible retarder arrangement, illustrated in U.S. Pat. No. 3,260,778, now expired. The web is pressed by a stationary surface (the "primary" surface) against a drive roll to provide a drive region, a stationary surface downstream of the drive region set at a substantial angle to the surface of the roll (the "angled retarder" surface) diverts the oncoming web through a substantial angle from its travel on the roll, and extending downstream from the primary surface, a thin flexible conforming surface (the "flexible retarder" surface) provides face-wise containment to the web as the web moves through the angle from roll surface to the angle of the angled retarder. By use of such a single roll geometry, a very small treatment cavity can be established that enables treatment of very thin webs and application of high pressures over short distances.
This angled retarder/flexible retarder arrangement seeks to achieve a balance between conflicting requirements. The substantial angle of the angled retarder enables an effective longitudinal compressive force to be applied to the web. Meanwhile, the flexible retarder, as it maintains the needed face-wise containment of the web while the web changes its angle of travel, also flexes to prevent choking of the travel of the treated web and to relieve excess pressure to prevent the web from snagging under the leading tip of the angled retarder blade.
In commercial devices built according to U.S. Pat. No. 3,260,778 the angle of the angled retarder has been about 38 degrees to the tangent to the roll and the flexible retarder that flexes to conform to that( angle has been a thin sheet of Swedish blue steel (e.g. 0.002 to 0.006 inch or 0.05 to 0.15 mm thickness).
A later machine using this principal, and further seeking to prevent snagging of the web beneath the tip of the angled retarder blade, is shown in Packard U.S. Pat. No. 4,090,385. In that machine, the roll is provided with grooves and the leading edge of the angled retarder is provided with spaced-apart mating fingers which are inserted into the grooves below the general surface of the roll. With this arrangement, variation in the treatment across the width of the roll may occur because the drive conditions are different at the grooved and non-grooved regions of the roll.
Longitudinal compressive treatment of webs using angled retarder/flexible retarder arrangements have been successful in certain commercial applications, though often the treatment has been limited to slow speed or to only a limited range of starting materials and products, and considerable operator skill often has been required in order to deal with changing production conditions.
A large number of cases have remained, particularly in the field of thin webs, in which commercialization has not occurred because of difficulty in setting up the treatment or in accomodating change in production conditions during running.
To give examples of changeable production conditions that can affect the opposed drive and retarding forces of the longitudinal compressive treatment and contribute to difficulties of initial set up or continued operation, we mention: change in the web-gripping character of the drive roll, for instance due to Wear of the drive roll surface or presence of foreign substances; variations in pressure of the web against the drive roll, due to change in the untreated web thickness or in the forces that press the confining surface and web against the drive roll or due to wear or change in the geometry of the confining surfaces; variation in the supply tension applied to the untreated web as it enters the treatment; change in the stiffness or softness of the untreated web as may occur due to change in moisture content or temperature of the original untreated web: change in the depth of the retarding passage through which the web passes; change in other retarder qualities due, e.g., to dimensional or speed change: and change in susceptibility of the web to its being retarded, e.g., due to change in the frictional qualities of the web to be treated; and so forth.
In production it has also been necessary to maintain precise alignment of the angled retarder. Such alignment may be difficult to maintain, and in some applications the alteration in treatment cavity dimensions resulting from slight misalignment may yield an unacceptably uneven product. For this reason, a rugged and expensive mounting has been considered necessary for the angled retarder/flexible retarder arrangement but still problems can occur.
Furthermore, during use of the angled retarder/flexible retarder arrangement for production, it has been critical to properly choose and maintain the flexible retarder to have it conform and apply proper resilient pressure to the angled retarder. Too little pressure applied by the flexible retarder, as may occur by wrong choice of its thickness, or due to wear, will prevent obtaining a desirable fine microcrepe effect. But with little change in the flexible retarder, a point is soon reached when too much pressure causes snags or tears by forcing material under the leading edge of the angled retarder. Improper alignment may put uneven pressure on the web, With a resulting unevenly treated product. And perhaps most disadvantageously, bending of the flexible retarder (e.g., repeated flexing during adjustment or use, or severe bending due to improper adjustment) can permanently deform the flexible retarder to introduce a permanent "set", reduce its pressure and resiliency, and cause the treatment to skip or end altogether.
As production conditions change during use of the angled retarder/flexible retarder arrangement, the point of treatment of the material under the low friction primary surface tends to shift forward or backward, and to affect the quality of the treatment. This requires backward or forward adjustment of the primary surface.
The job of the person operating the machine has been to take all production conditions into account when establishing the initial running adjustments of the treatment and, during operation, to observe changes in the conditions as they occur and to attempt to counteract these changes by compensatory adjustments. In practice, more than one variable production condition can change at the same time, producing a complicated behavior that the operator of the machine must seek to accomodate.
For the microcreping applications that have been commercialized, uniformity of treatment is often a critical requirement, and failure to make appropriate timely adjustments may harm the product. By way of example only, in producing disposable medical products such as surgical drapes, a large number of microcreped fabric sheets may be stacked so that a number of pieces are cut at the same time. If the sheets are not uniform, and therefore will nor lie flat, the cut will be uneven, producing misshapen articles.
Similarly, kraft paper used as a separator between stacked sheets of steel must be uniform to keep the pile of steel sheets flat on a pallet.
In another case, the softening of wadding of original thickness of the order of 0.001 inch (0.025 mm) requires extremely high speeds of treatment to be practical, Which may generate excessive heat that cannot be tolerated by the angled retarder/flexible retarder arrangement or the web being treated.
One important object of the present invention is to provide new techniques for longitudinal compressional treatment of webs which have the advantages of a single roll, bladed configuration but which reduce or eliminate the various critical features of the treatment. Another object is to enable uniform, high quality treated web products to be obtained with a wide range of materials and thicknesses, and especially with very thin webs. Another object is to provide a technique that enables use of relatively heavy, long-wearing elements capable of extended operation even at high speed. Another object is to provide a machine of improved simplicity of construction. Other objects of the invention are to achieve increase in production and energy efficiencies, and novel specific treatments for web materials. One specific object of the invention is to provide an improved method of shrinkproofing webs, for instance heavy diagonal weave fabrics such as cotton denims.